Methods of coating an analytic substrate, (also referred to herein for example as a microscope slide or analytic plate), with chemical compositions that enhance the adhesion of biological specimens (e.g., specimens such as cells, tissues, fluids, biological micro-molecules and macro-molecules) to the analytic substrate are well known. Originally, analytic substrates were often coated by dipping them in common proteinaceous materials like gelatin or albumin. These compositions would provide the analytic substrate with a weak adhesive property for adhering the biological specimen to the analytic substrate. However, because there was a need for an enhanced adhesive effect, the process of coating analytic substrates evolved to use other procedures and materials, for example utilizing polymers of positively charged amino acids such as L-lysine (i.e., poly L-lysine). In this method, the analytic substrate was dipped into a 2 to 5 percent solution of poly L-lysine dissolved in a common laboratory solvent such as an alcohol or acetone. These methods produced analytic substrates having improved adhesive properties, but they proved to be inadequate when used with newly developed procedures in the laboratory which subjected the analytic substrate, with the biological specimen attached thereto, to extremely harsh environments or conditions such as enzymatic digestion, microwave boiling, pressure cooker treatments, steamer boiling, and in-situ hybridization protocols.
The composition most often used today for making positively coated analytic substrates which are able to withstand the most demanding laboratory procedures is the silicone polymer 3-aminopropyltriethoxysilane. The term “positively charged analytic substrate”, as used herein, relates to the “positive” electrostatic charge the coating imparts on the glass surface. This “positive” net charge of the coating attracts the typically “negative” net charge of the biological specimen.
The method commonly used today for producing a positively charged analytic substrate (also referred to herein as a “coated analytic substrate”) in a laboratory setting is to dip the analytic substrate in a 2% percent solution of 3-aminopropyltriethoxysilane in acetone for 2 to 10 minutes. The analytic substrate thus treated is then rinsed in either several changes of deionized water or fresh acetone and is then air dried at room temperature, or heated for example at 60° C. for 60 minutes, or overnight. The coated analytic substrates are then stored in a dust free container at room temperature until used in the lab.
To carry out this procedure, laboratory personnel must spend significant amounts of time unpacking plain “untreated analytic substrates” and placing them into analytic substrate racks (e.g., microscope slide racks) which separate individual analytic substrates from each other so that all surfaces of each analytic substrate can be coated. This cumbersome manipulative procedure of taking each individual analytic substrate from its original packing, placing it in a rack, dipping it into the coating solution, rinsing it several times, then drying, and repacking the analytic substrates for storage has proven not to be cost effective for most laboratories. Further, the quality of the coating on the analytic substrate produced in this way varies due to known variables which are uncontrollable, and unknown variables that arise during the process, such as differences in concentrations among batches of purchased coating compositions, differences in concentrations of batches of working coating composition solutions prepared by different personal, differences in the types of mixing equipment used (i.e., pipettes vs. graduated cylinders), calibration variation, temperature changes, and degradation of the working coating solution during use.
Furthermore, when time protocols are not strictly followed during the coating process, several inconsistencies in the charged coating on the analytic substrate can result among batches of coated analytic substrates. For example, an “undercoated” or “undercharged” analytic substrate results in poor adhesion of the specimen to the analytic substrate thereby leading to detachment of the specimen from the analytic substrate, an obviously undesirable occurrence. “Overcharging” or “overcoating” the analytic substrate by increasing the concentration of the coating solution applied to the analytic substrate, or by increasing the time of treatment, often renders the analytic substrate extremely hydrophobic (“low wettability”) such that the analytic substrates exhibit decreased or unimproved adhesion characteristics and may cause non-specific attachment to the analytic substrate of testing chemicals (e.g., dyes and pigments) used for the visualization of the specimen. An excessively hydrophobic condition is detrimental to automated staining instruments that require the analytic substrate to maintain its wettability since as the positive charge of the analytic substrate increases, so does the hydrophobicity (liquid repellancy) of the analytic substrate.
These inherent problems in quality consistency of the analytic substrate coatings are due to a high degree of human involvement necessary to produce these coated analytic substrates. Therefore, since there is an overwhelming demand by technicians for these types of positively charged coated analytic substrates on a daily basis, laboratories have opted to purchase quantities of ready-to-use charged analytic substrates from commercial laboratory supply companies. Unfortunately, all of the problems and inconsistencies in quality are still experienced in these commercially available analytic substrates even after the best efforts of assembly line production of coated analytic substrates from these vendors.
For example, the dipping process used by manufacturers generally produces an uneven coating on the surface because after the analytic substrate is dipped into the working concentration of the coating, the coating material on the analytic substrate is diluted during the rinse steps thereby often producing an uneven coating. Uneven drying conditions further produce the uneven coating. Even with increased concentration and/or increased time, there is a diminishing return since the ability of the coating composition to bind to the glass surface is partially based on the physical limitations of the chemical entity being in intimate contact with the glass surface. Furthermore, it is known in the art that the prior art process of dipping the analytic substrates into the coating composition produces a analytic substrate that is coated on all surfaces of the analytic substrate. This is wasteful, because only one analytic substrate surface, herein referred to as the “functional side,” “specimen side,” “upper side,” or “upper surface” needs to be coated for use.
These inconsistencies in quality cause discouragement and frustration in the laboratory personnel who purchase these ready-to-use coated analytic substrates. There is therefore a worldwide consensus regarding the need for an improved coated analytic substrate that imparts adhesion properties which are superior to the current laboratory coated or commercially coated analytic substrates, but most importantly which is reproducible and consistent in quality and function.